[HELP] ECM or TPS maybe??

[OdnsRvns]

1991 Max 2.4L 2WD 4G64

OK hey guys after putting my first tank of fresh gas in my Max that was sitting for 3 years I'ts developed a engine miss. Now before we go and blame the gas because that's where I started as well I tried a tank of HEET to eliminate water and have ran it down to almost fumes and the problem persists. Second Full tank of gas still does it, and the third tank as well. I am also ruling out a FILTER/Pump issue because when I get on it the truck runs fine.

The issue I'm having is it misses and lurches when I'm just barely on the throttle trying to hold a constant speed. Its worse at lower RPM's and in Lower Gears but its all speed ranges. This truck was over heated by the previous owner and I just had the head redone and it starts first crank always. The timing is good and its got a new Cap, Rotor, Plugs, and O2 Sensor (I changed these out when we did the head).

So knowing this truck came from Utah and been in that desert heat, Its been over heated, and its sat for 3+ years here in the Midwest, I'm leaning toward something in the electrical causing my issue. My first two things that when I search that come closest is the ECM or TPS. Give me some advice on how to root out which is the culprit or even what may be the culprit. Both these parts are ridiculously expensive at a parts store so I'm going to most likely have to online or buy used. Is there something I'm missing that I haven't thought of or should check. Help me out!

[OdnsRvns]

Also forgot to mention I can smell the gas after I drive for a bit. I've looked everywhere for a leak to no avail dry as a bone.I get a little black smoke when I start up sometimes. Makes me think I'm running super rich since my fuel economy for a 4cyl seems like shit. Hope I've provided enough details for everyone!

[mitchi]

I have the same thing happening.

Posting to see what answers you get.

Thanks

[Jeff V.]

How about a possible clogged or stuck injector? Have you pulled your spark plugs out to see if any of them have deposits or residue that look different from the other ones?

TPS is easy enough to test with a multi meter. From your symptoms, I'm guessing that's not it though.

[OdnsRvns]

i pulled the wires off the each plug and the engine still missed the same way i couldn't narrow it down to one cylinder. Ill pull the plugs and test the sensor when I get home tonight. I didnt know it was so easy to test the TPS.

[Rahtid]

Could be the coolant temp sensor

[OdnsRvns]

90 might max ecmpng.jpg
Well pulled the ECM/ECU today and here I am thinking I've found my problem. I could smell the circuits before i even got the screws out of the side. I'm a hobby computer guy but I'm try an solderer this board with some new parts to see if that fixes it what do I have to loose right? I know and find the capacitors that need replaced can anyone Identify what the little square box is thats all burnt up in this photo. I'm not even sure that can be replaced.

[OdnsRvns]

Imgur of the same image can see it a little better.

http://imgur.com/a/U3Nqn

[OdnsRvns]

How about a possible clogged or stuck injector? Have you pulled your spark plugs out to see if any of them have deposits or residue that look different from the other ones?

TPS is easy enough to test with a multi meter. From your symptoms, I'm guessing that's not it though.

I know its late now to post this but injectors are ticking as they should all at the same rate. And plugs are brand new and are sparking when I pulled them. I think its the ECU itself is bad see my post above!

[Jeff V.]

The little square thing is just a surface mount capacitor. If there are no numbers on it, it'll be tough to find a replacement.

I've got a couple of 4G63 ECUs in my box of parts. I'll check those and see if they're similar. Maybe they'll have some markings.

[OdnsRvns]

Just wanted to update this for anyone searching this and may find this post. I was able to swap the ECM/ECU out with one from a 94 95 Mighty max and the truck runs great. It was a literal plug and play no funny business at all. My truck is a 1990 so the 94-95 ECU worked even thought the model numbers on the ECU's are different. I'm also running a RPM tachometer with no issues everything works fine. I'll keep updating if anything changes but as of right now my MM is running great!

[OdnsRvns]

This was the ECM i bought off ebay for anyone wondering

http://www.ebay.com/itm/182407279618...%3AMEBIDX%3AIT

[DroppedMitsu]

That shouldn't work properly, are you sure you are not throwing any codes? The 90 truck uses a different MAF(air sensor, it has one less wire than 91up trucks) so I'm pretty sure your ECU is not able to read your MAF correctly.

[Jeff V.]

DSM and 3S guys swap MAFs around all the time. They're electrically compatible. But they key there is they can edit the necessary ECU values in flash or EEPROM to get the calibration back into spec.

I think the old trash can MAFs are close enough to the newer plastic ones that it'll run ok. Might just be a little lean. It should be ok for a naturally aspirated engine.

[OdnsRvns]

That shouldn't work properly, are you sure you are not throwing any codes? The 90 truck uses a different MAF(air sensor, it has one less wire than 91up trucks) so I'm pretty sure your ECU is not able to read your MAF correctly.

A far as I can tell its running well. I don't have any maintenance lights popping up. I'd have to check my registration one more time maybe I actually have a 91?? Either way back up and going and onto getting new wheels.